It's possible. I turn my HTPC (XBMC-Live) on and off with my imon remote. However, the receiver is an Antec Multimedia Station Elite with a built in vfd and sits between the power supply and motherboard.

I'm not sure about powering a computer on with a remote. The computer has to keep the usb device "hot" so that it can receive the instruction. However, it should be pretty easy to set your remote up to wake your OS from suspend or hibernate.